which appears to most people to say:
"Extension in MM = constant force in Newtons"
I think he was trying to say
Extension in MM / Force in Newtons = constant
I stand corrected. This does not change the fact that this fromula has
nothing to do with a plane hitting a building.
Hooke's law is most often used in small displacement approximations, such as a pendulum swinging over a small angle. This comes from:
F = -dU/dx where U is the potential energy and x is the displacement.
This means that where U is a parabola, F = kx by integration. Assume that x0 is a local minimum of U and U has a taylor expansion:
U = U(a) + U'(x - a) + (1/2)U"(x - a)^2 + (1/6)U'''(x - a)^3 + ...
Since U(a) is a local minimum:
U = U(a) + (1/2)U"(x - a)^2 + (1/6)U'''(x - a)^3 + ...
as U'(x-a) = 0. Assume (x-a) is small st (x - a)^2 >> (x - a)^3
Then
U = U(a) + (1/2)U"(x - a)^2 and F = -dU/dx = - U"(x - a) which is Hooke's law.
Contrast this scenario (small deviations around a local minimum) with that of a large jet plowing into the side of a building and you can clearly see how ridiculus an appeal to hooke's law is. Even more foolish than the clowdy day claim or the pedophilia allegations. Even if you were to hit a WTC sized slinky with a plane that has a giant spring on its nose hooke's law would probably not come up.